1. Field Of The Invention
This invention relates to filled polymeric masses and more particularly relates to filled thermoplastic polymer matrices and to additives integrally added to the filler thermoplastic polymer blend for conserving or enhancing the physical properties of the filled thermoplastic polymer including improved impact strength. The invention also relates to novel integral additives for addition to filler-thermoplastic polymer blends for providing improved processing characteristics to the blend such as lower pressures required to fill molds in an injection molding operation. The invention also provides methods for producing reinforced or filled thermoplastic polymers of improved physical properties and relates to the resulting improved filled thermoplastic polymers.
2. Description Of The Prior Art
A very extensive amount of research has been performed on the treatment of fillers or reinforcing agents for synthetic polymers including thermoplastic polymers such as polyethylene, polypropylene and the like. Much of this research has been centered on pretreatment of the fillers with coupling agents such as gamma-methacryloxypropyl trimethoxysilane as described in U.S. Pat. No. 3,663,493; tetravinylcyclotetrasiloxane as disclosed in U.S. Pat. No. 3,859,247; mercapto-propyl or glycidyl propyl trimethoxysilanes as disclosed in U.S. Pat. No. 3,853,692; a diol comprising polyoxypropylene block sandwiched between two polyoxyethylene blocks as described in U.S. Pat. No. 4,017,452; maleic or methacrylic acid esters of polyether polyols as described in Belgian Pat. No. 879,092, and others. The pretreatment of fillers requires high shear mixing of the coupling agent with the finely divided filler which consumes large amounts of energy, time and extra processing, all of which is economically unattractive and contrary to energy conservation efforts.
Integral blending techniques (also called in situ addition) have also been widely used whereas coupling agent or surface treatment agent is added to a stirred mixture of polymer and filler. Integral blending however requires larger quantities of the coupling agent or surface treatment additive and is dependent on the specific type of filler and resin for success. In addition mixing time heretofore was quite extensive in the integral blending technique because the coupling agent requires time to migrate to the filler surface and react and condense there as described in the article, "Surface Modification Of Fillers And Reinforcement In Plastics", by E. P. Plueddemann and G. L. Stark, published by The Society of the Plastics Industry, Inc., 32nd Annual Technical Conference, 1977, (Sec. 4-C, pages 1-9). This article refers to a study of commercial surface active agents as used in the paint industry such as fatty acids, phosphate surfactants and the like in the hopes of developing a system in which one basic silane coupling agent on all fillers can be used and then modified as needed as surface active additives to obtain compatibility with individual polymers. However, the article fails to disclose any achievement of success with that approach and it may be assumed that the approach is still being researched.
There are considerable problems in using surfactant or wetting agents in integral or in situ additives. The article, "Hydrophobic Filler Wetting A New Technique For Improved Composite Performance And Production", by D. E. Cope, published by The Society of the Plastics Industry, Inc., 34th Annual Technical Conference, 1979, (Sec. 24-E, pages 1-3) discloses that surfactants generally do not react chemically at the filler surface and in fact they may be fugitive and may often result in porosity or bubbles and cites, as typical surfactants, sulphonates, phosphates and silicone oils. The article further states that the surfactants tend to cause adverse side effects.
Furthermore, U.S. Pat. No. 4,251,576 states in column 22, lines 22-27, that the use of nonyl phenol/ethylene oxide condensate in a monomer filler mixture flocculated the mix and resulted in a cracked,flawed casting.
In the article, "Effect of Polymeric Additives on the Rheological Properties of Talc-Filled Polypropylene", by D. C. Goel, published in February 1980, Polymer Engineering and Science, Vol. 20, No. 3, pages 198-201, work is reported in blends containing polypropylene, talc and an oligomer of polypropylene oxide were extruded twice on a single screw extruder for uniform distribution of the oligomer throughout the polymer/filler matrix. It was noted that at the level of 3 wt. % of oligomer in the polymer/filler matrix provided a decrease in viscosity and also provided a decrease in the elasticity of the filled polymer composite which suggests a possible reduction in impact properties.
The general teachings in the prior art therefore generally discourage the addition of surfactants to polymer/filler blends.
The Bixler et al U.S. Pat. No. 3,471,439 discloses finely divided non-reinforcing fillers, the particles of which are coated with an organic compound having a chemical affinity for the filler surface such as a material having at least one ethylenic unsaturation, with an organic compound having at least two polymerizable ethylenic unsaturations and a free radical generator. The filler then is dispersed in the thermoplastic polymer and the unsaturated material is polymerized to bond the filler to the polymer. The patent also discloses that saturated surface active compounds such as stearic acid, calcium stearate and the like can be used, particularly if they possess one or more carbon atoms from which a hydrogen atom can be abstracted by a free radical.
None of the prior art references identified above discloses or suggest any method that involves the addition of a surfactant of the type described and claimed herein to a mixture of thermoplastic polymer and filler for the purpose of improving processing characteristics such as pressure-to-fill requirements and conserving or enhancing physical properties.